Sana Seraj — Year 3
Mentor: Teresa Seifried, Serena Chin
Introduction
According to the United Nations Environment Programme, eight million tonnes of plastic end up in the ocean each year, which can be ingested as microplastics by marine life (UNep, 2017). Microplastics can absorb organic toxicants from the sea surface microlayer, relaying harm to organisms that ingest them. Additionally, microplastics accumulate in tissues as organisms are unable to digest them. This allows the chemicals to biomagnify and create harm at even higher levels in the food chain (Costigan et. al, 2022).
Existing methods to remove microplastics from water are limited in sustainability or efficiency (Sayam et al, 2025). While previous research on marine microplastic mitigation has provided valuable insight into colloidal-based microplastic removals, many procedures use reagents that are harmful to marine life and non-biodegradable (Srinivasan et al, 2025). Conventional methods of microplastics removal rely on flocculation. Flocculation clumps small particles suspended in water into a bigger particle called a floc using chemicals called flocculants (Malvern Panalytical, 2024). Common flocculants aluminum sulfate and ferric chloride are harmful to aquatic life if swallowed, causing long-lasting effects (Safety Data Sheet, 2015, Safety Data Sheet, 2022). Consequently, biopolymers are an eco-friendly alternative (Eco-Friendly Water Treatment, 2024).
Plant-based flocculants like chitosan, tannins, cellulose, alginate, gums and mucilage have been investigated as potential substitute flocculants (Satle et. al, 2012). However, studies on Xanthan gum are rare despite its potential. Xanthan gum (XG) is plant-based flocculant which is a cheap, effective emulsifier commonly used in cooking that’s widely accessible (Pullen, C., 2025). It has a cellulose backbone and trisaccharide side chains of mannose and glucuronic acid, and is made by fermenting the bacteria Xanthomonas campestris (Vardhan et al, 2025). This structure allows it to be a very effective stabilizing agent. It also allows for strong thermal stability (Kulkarni et al, 2015). The effectiveness is due to its carboxyl groups that help make large flocs by conferring charges (Oropeza-Guzmán, M. T., & Araiza-Verduzco, F., 2023). The carboxyl groups provide ionic interactions and advanced bridging between the flocculants, these molecular interactions allowing for polymer bridging and coagulation (Yang et al, 2024). Studies such as sudirgo et al. found XG to be an effective coagulant aid as removal efficiency increases with XG concentration. Thus, this study is based on observing the effects of a natural polysaccharide (xanthan gum) as a flocculant for microplastic capture, due to its renewable, sustainable nature.
This study aims to establish XG as an effective flocculant to capture various polymer types from water. Through the past research indicating that XG holds promise as an alternative to current flocculants, we aim to show that an XG concentration as low as 3% w/v efficiently removes PET and PP microplastics from solution. Thus, we establish XG as a viable flocculant for use in marine systems and hope to establish more widespread use.
Materials and Methods
Microplastic samples:
This study utilized polyethylene terephthalate and polypropylene as the model system for plastics removal. We provide an overview of the samples shared with us by our collaborators at UBC.
Table 1 overviews the microplastic samples used. Our collaboration partner from UBC shared these samples with us. They purchased polyethylene terephthalate (Nanochemazone) and Polypropylene (Goonvean Fibres Ltd).
Table 1: Detailed information about the microplastic samples used in this study.
| Polymer Type | Structural Formula of Monomer | Vendor | Size (diameter) |
| Polyethylene terephthalate | Nanochemazone (CAS: 25038-59-9) | 80 μm | |
| Polypropylene | Goonvean Fibres Ltd (CAS: HM20/70P) | 60 μm |
Figure 1: Light Microscopy Images of the Studied Microplastics, A- Polyethylene terephthalate, B-Polypropylene.
Methods
Figure 2: Graphical Representation of Microplastic Removal Workflow
Only one quadrant out of the 4 was counted and it was assumed that the count was uniform across.
Microplastic Suspension Preparation
A 2.5 wt% (w/v) aqueous suspension of microplastics was prepared by adding 0.25 g of microplastic powder to 9.75 mL of distilled water (Great Value) in a 100 mL beaker. 2 microplastic solutions were prepared for each polymer type to retain a control sample.
Experimental Treatment
0.02 mL of benzyl benzoate was added to each microplastic solution. This was added because benzyl benzoate is a known plasticizer, which increases polymer chain flexibility, allowing for enhanced polymer bridging (Pharmaceutical Research and Production Company and Libretexts, 2023). Samples were then stirred with a magnetic stirrer (Bipee, figure below) for 5 minutes at approximately 100 rpm.
After 5 min, the samples were heated to 70 ℃, because heat allows for the plasticizer to diffuse better in the polymer (Jinli Chemical). Once 70 degrees was reached, the heating was stopped and the beakers were stirred for another 15 min. After time expired, the beakers were removed from stirring and cooled in an ice bath to ambient temperature. Once the solutions reached room temperature, 0.029 g of xanthan gum powder was added to the experimental beaker and both beakers were immediately stirred for 45 min each. The beakers were removed from the magnetic stirrer, and 10 µL aliquots were removed from the bottom of the beaker at 0, 15, 30, and 45 min. These samples were transferred to a hemocytometer and microplastics were counted under a microscope using a 10X objective.
Microplastic quantification
A Neubauer improved hemocytometer with chamber dimensions of 3×3 1 mm2 squares, with a depth of 0.01 mm was used to count the number of microplastics one quadrant by using a microscope at 10x. Hemocytometers are specialized glass microscope slides used for counting cells (ThermoFisher). They hold specific volumes, allowing reproducible and accurate cell densities to be obtained. In this case instead of cells microplastic samples were counted on the specific grid lines. After 10 μL of solution was pipetted into the hemocytometer, particles in the hemocytometer’s top right grid were counted, and it was assumed that the count was uniform across the other three (Fig. 3). When xanthan gum was viewed in the hemocytometer, no spherical objects to be confused with microplastics were seen (Fig. 4).
Figure 3: Diagram of a hemocytometer showing which lines where the areas where microplastics were not counted.
Figure 4: Light Microscopy Images of the XG solution (the matrix) at 10x objective.
Results and Discussion
Comparison of Polymer Types
Refer to supplemental for raw data
Formula:
Particles/L = (4 x particles counted in raw data of one quadrant)/ 0.4μL)x 1,000,000 μL/L
0.4 μL was used because the volume of one quadrant is 0.1 and 4 of them mean 0.4 μL.
| Polymer type | Sampling Time (min) | Particles/L in Experimental Sample (bottom) | Particles/L in Control (bottom) |
Polypropylene (PP) | 0 | 2.6 x 108 | 3.0×107 |
| 15 | 0 | 1.3×108 | |
| 30 | 1.0×107 | 9.0×107 | |
| 45 | 3.0×107 | 6.0×107 |
% Difference= ((Particles at Time X in experimental/1 L)/ (Particles at time X in control/1 L)) x 100
At 0 min: 2.6×108/3.0×107 X100 = 866.67%
At 15 min: 0/1.3×108 X100 = 0%
At 30 min: 1.0×107/9.0×107 X100 = 11.11%
At 15 min: 3.0×108/6.0×107 X100 = 50%
The trend observed was that at time 0, the experimental had a higher particle concentration on the bottom, yet as time went on from 0 to 45 minutes, the amount of particles at the bottom went from 866.67% to 50%, demonstrating that XG has an effect on the the amount of particles free-floating at the bottom.
| Polymer type | Sampling Time (min) | Particles/L in Sample (bottom) | Particles/L in Control (bottom) |
Polyethylene Terephthalate (PET) | 0 | 1.5×108 | 1.0×107 |
| 15 | 1.0×107 | 0 | |
| 30 | 0 | 0 | |
| 45 | 3.0×107 | 0 |
% Difference= ((Particles at Time X in experimental/1 L)/ (Particles at time X in control/1 L)) x 100
At 0 min: 1.5×108/1.0×107 X100 = 1500%
At 15 min: 1.0×108/0 X100 = 0 %
At 30 min: 0/0 X100 = 0 %
At 15 min: 3.0×108/0 X100 = 0 %
A similar trend was observed like PP, in PET the average amount of particles in the experiment was higher, but as time went on there the amount dropped rapidly, indicating a reduction in the amount of free-floating particles available.
| Polymer type | Sampling Time (min) | Particles/Lin Sample (bottom) | Particles/L in Sample (top) | Particles/L in Control (bottom) | Particles/L in Control (top) |
Polyethylene Tetrathylene | 0 | 2.0×107 | 3.0×107 | 1.0×108 | 0 |
| 15 | 1.0×107 | 1.0×107 | 0 | 0 | |
| 30 | 4.0×107 | 2.0×107 | 0 | 0 | |
| 45 | 2.0×107 | 1.0×107 | 2.5×108 | 0 |
% Difference= ((Particles at Time X in experimental/1 L)/ (Particles at time X in control/1 L)) x 100
Top:
At 0 min: 3.0×107/0 X100 = 0%
At 15 min: 1.0×107/0 X100 = 0%
At 30 min: 2.0×107/0 X100 = 0%
At 15 min: 1.0×107/0 X100 = 0%
Bottom:
At 0 min: 2.0×107/1.0×108 X100 = 20%
At 15 min: 1.0×107/0 X100 = 0%
At 30 min: 4.0×107/0 X100 = 0%
At 15 min: 2.0×107/2.5×108 X100 = 8%
A similar trend to the other PET trial was observed, at time 0 the experimental to control had a higher particle amount than at the end of the trial.
Comparison of Sample Location
The trend overall for the controls was that the particle amount was relatively stable throughout the trial, having a gradual shift to more particles on the bottom as gravity pulled the particles down (fig. 5).
Figure 5: Plot of the data of the overall data of the all the controls throughout the trial (raw data)
For PP, the trend for the XG sample one was that the number of free-floating particles lessened over time. Since floc formation , which is smaller particles (microplastics) coming together to make a larger particle (a floc), as more flocs formed over time, the number of particles available for testing on the bottom had a general trend of decreasing over time (Malvern Panalytical, 2024). This is due to the fact that the pipette cannot get a floc into it, so all the data received is presumed to be a small free-floating microplastic (flocs are too big to be observed at the specific magnification of microscope used) (Fig. 6).
Figure 6: Plot of the data of the PP trial (raw data)
For the PET, the number of free-floating particles obtained over time lessened, indicating that flocs were forming due to less particles being available for observation. The overall trend on top of the XG sample was that over time the number of microplastics on top lessened (fig. 7).
Figure 7: Amount of microplastics in the PET trials over time (raw data)
This could indicate that as time passes, floc formation occurs and the microplastics sediment, due to gravity having a larger effect on the now larger particles (fig. 8 and 9).
Figure 8: Plot of the first PET trial (raw data)
Figure 9: Plot of the second PET trial (raw data)
Future Directions/Conclusion
As the amount of microplastics in the oceans per year rises to unprecedented levels and our current flocculants fail to be sustainable, this research is relevant in the forthcoming work world-wide to find natural alternatives. Our research shows promise in the ability to capture microplastics using natural flocculants. Further research may look into different pH levels with XG, due to the fact that the ocean has different pH’s at different places. Given more time and money, more trials can be done looking into different salinities, since the ocean has freshwater and salt water, or look into different temperatures such as what happens at a higher oceanic temperatures. All of these different factors can show that XG is a robust coagulant for microplastics across a multitude of scenarios, proving it to be useful in the fight against microplastics in aquatic environments.
Supplemental
Table 2. Provides the overall trend of the effect of xanthan gum on the microplastic polypropylene.
Table 2. Microplastic count at different time stamps from the control and experimental (sample).
| Polymer type | Sampling Time (min) | Total Count in Experimental Sample (bottom) | Total Count in Control (bottom) |
Polypropylene (PP) | 0 | 26 | 3 |
| 15 | 0 | 13 | |
| 30 | 1 | 9 | |
| 45 | 3 | 6 |
Table 3. Provides the overall trend of the effect of xanthan gum on the microplastic polyethylene terephthalate .
Table 2. Microplastic count at different time stamps from the control and experimental.
| Polymer type | Sampling Time (min) | Count in Sample (bottom) | Count in Control (bottom) |
Polyethylene Terephthalate (PET) | 0 | 15 | 1 |
| 15 | 1 | 0 | |
| 30 | 0 | 0 | |
| 45 | 3 | 0 |
| Polymer type | Sampling Time (min) | Count in Sample (bottom) | Count in Sample (top) | Count in Control (bottom) | Count in Control (top) |
Polyethylene Tetrathylene | 0 | 2 | 3 | 10 | 0 |
| 15 | 1 | 1 | 0 | 0 | |
| 30 | 4 | 2 | 0 | 0 | |
| 45 | 2 | 1 | 25 | 0 |
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